Implantable medical tissue stimulators including pacemakers, defibrillators and neural stimulators are used to stimulate tissue such as cardiac tissue or spinal cord tissue with electrical pulses. Such tissue stimulators are now quite common and typically include a hermetically sealed housing or can containing an electronic circuit and power supply for producing electrical impulses under control of a programmed microprocessor. The pulse generator is connected to target tissue by means of a suitable medical lead. Such leads typically include an elongated flexible lead body having a proximal end and a distal end. Disposed at the distal end of the lead are one or more tissue contacting electrodes. The electrodes are connected by wires running through the lead body to associated contacts on a terminal pin at the proximal end of the lead.
The proximal lead terminal pin is adapted to be inserted into a longitudinal bore formed in a header of the stimulating pulse generator. Contained within the header are one or more conductive connector blocks that are connected to feedthrough pins that pass through hermetic seals to join with input and/or output nodes of the electronic circuit contained within the housing. The connector blocks will typically have apertures formed therethrough in alignment with the bore of the header, allowing the proximal lead terminal pin to be inserted through them. To lock the lead in place, the connector blocks will typically include a threaded bore that extends transverse to the longitudinal direction of the bore in the header. Setscrews are inserted into these threaded bores and tightened down against contact areas on the proximal lead terminal. In prior art connector block designs, from time to time the setscrew is accidentally backed out completely from the block and could not be re-inserted in to the block. Another equally problematic situation occurs when the lead is not inserted in the connector block and the setscrew is advanced to the extent that it falls into the longitudinal bore of the block which is an extension of the longitudinal lead receiving bore of the header.
U.S. Pat. No. 5,989,077 to Mast et al. provides an example of a header assembly of the type which the present invention seeks to avoid. Specifically, the header assembly serves for coupling a cardiac lead to a cardiac stimulator and employs a setscrew threadedly coupled to a connector housing of the header assembly but without provision for retaining it in place so that it neither backs out of the tapped bore in which it is received or advances too far in the absence of an end of a lead which it is intended to engage.
In U.S. Pat. No. 5,000,177 to Hoffmann et al., an implantable system is provided in which setscrews are confined within bores of the connector block against advancing too far but, notwithstanding the provision of plug seals over their heads, are capable of being backed away from their threaded condition.
In U.S. patent application Publication US 2004/0225334 to Persuitti et al., a connector block and its associated locking setscrew for an implantable electronic tissue stimulating device are designed to eliminate thread damage to the setscrew which is a cause of the setscrew becoming stuck in the connector block. In this disclosure, there is no concern presented for the problem addressed by the present invention.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.